Car idles very high when first started then a loud humming noise mechanic says its an air diverter valve

Check the hose that goes to the pcv valve, If it gets soft it will vibrate and hum.

Humming Noise Front End- Any Ideas? - Ford Explorer and Ranger ...

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Dec 18, 2008 - 19 posts - ‎16 authors
Have a 98- Eddie 4.0 SOHC, 4WD with a 100,000 mi. When driving it has a humming noise, it almost sounds like a bad tire, or a ... I start to hear the humming noise at 20 mph, it is very loud at 40 to 50 mph ... 94 XLT-95 FX4. humming gets louder as speed increases
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I would start with the pcv valve and tube

Check the vacuum hoses for leaks. Follow them around and make sure they're all connected and not worn out to where they had fallen off due to the hoses being old and worn out. Take some soapy water in a spray bottle and spray mist the intake and see if the idle changes. Check the big hose coming from the brake booster to the intake and make sure it's connected and in good shape. Basically check everything for vacuum leaks. It sounds like that's what you're issue is.

too little information to go by..humming noise..what year/model/engine etc....

however i assume it s a ford and it is most likely caused by a sticky idle air control valve...they tend to hum and "hoot" when sticking, this may be associated with stalling at idle and/or hard starts unless aplying gas pedal. you can identify the idle air control valve as it is attached to most of the engnies by 2 botls and has about a 3-4" silver tube extending abaw from bolts, it is on top of the engine. when these make noise and backfeed through the air box a vibration can be felt from it. there will be a wire goinf to the valve, unplug it whil engine is running and when you hear the humming..if noise gone once it is unplugged...replce it WITH A FACTORY PART!!!

hope this helps

Take all of the belts off for a short run at idle. If the sound goes away it is pulley related, spin each pulley and listen for bearing noise, also check for play at this time.

If the noise does not go away when the motor is driving no accessories you have a more serious problem.

the idle air bypass valve is making noise and resonating through the air inlet the valve needs to be replaced there is also a revised hose to the valve to reduce noise if it hasn't already been replaced

Replace "idle speed motor" (also known as idle air contrl valve).

It sounds like the cylinder is part of the emission control system. It is probably a valve which is stuck inside. Remove it and clean it with wd-40. If this doesn't work, let me know.

I had experienced the same problem with my 93 TC. I'll try to make it short. Replace the Idle Control Valve. Cost me $50 at AutoZone. It has a electronic plunger that has a rubber o ring on the end of it. It separates two air chambers inside the valve. When the rubber gets old and the plunger is suppose to cut off the air coming in from one chamber to the other, the air gets sucked between the chambers across the old rubber causing the humming noise. That is also why the engines revs up and down and wont idle right. It is located between the firewall and the back of the motor just to the left (drivers side) of the throttle control assembly. When you look up on the internet on how to replace it, it will tell you to remove all the housing surrounding the wiper blade control arms and assembly so that you can access it. If you take your time, just remove some of the hoses and wires connected around it and you can access it without removing all that ****. Only has two screws to it that point up and can be reached with a ratchet and extension. Car runs great now and finally got rid of that noise.